#include<stdio.h>
#include<math.h>
int main()
{
 	int sign=1;
 	double pi=0.0,n=1.0,term=1.0;
 	while(fabs(term)>=1e-6)
 	{
 		pi+=term;
 		n+=2;
 		sign=-sign;
 		term=sign/n;
	}
	pi*=4;
	printf("pi=%10.8f\n",pi);
 	return 0;
}

